A perovskite-type oxide of Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCFO) shows mixed (electronic/oxygen ionic) conductivity at high temperatures. Membrane made of the oxide has high oxygen permeability under air/helium oxygen partial pressure gradient. At 850 degreesC, oxygen permeation rate maintained about 1.15 ml/cm(2) min for more than 1000 h under ambient air/helium oxygen gradient. A membrane reactor constructed from the oxide membrane was applied for the partial oxidation of methane (POM) to syngas, LiLaNiOx/gamma -Al2O3 with 10 wt.% Ni loading was used as the packed catalyst. At the initial stage, oxygen permeation rate, methane conversion and CO selectivity were closely related with the state of the catalyst. Less than 21 h was needed for the oxygen permeation rate to reach its steady state. A membrane reactor made of BSCFO was successfully operated for POM reaction at 875 degreesC for about 500 h without failure, with methane conversion of > 97%, CO selectivity of > 95% and oxygen permeation rate of about 11.5 ml/cm(2) min. Under membrane reaction condition, the POM reaction mechanism was suggested to obey the CRR (complete combustion of CH4 to CO2 and H2O and a subsequent reforming reaction of the residual CH4 and with CO2 and H2O to CO and H-2) mechanism. (C) 2001 Elsevier Science B.V. All rights reserved.